The present invention relates to a wind-driven energy-generating device of the type including a turbine having rotor blades driven by the wind. The invention is particularly useful with respect to aerogenerators for generating electrical power from the wind, and is therefore described below with respect to this application.
The many designs heretofore proposed for utilizing wind power for generating energy usually suffer from either low efficiency and/or high capital cost and therefore almost none have reached any significant commercial use. More recently, it has been proposed to utilize shrouds including a throat within which the wind-driven rotor blades are mounted for rotation, an intake section upstream of and converging towards the throat, and a diffuser section downstream of and diverging away from the throat. Such shrouds can increase the power output of a turbine by a factor of about 3, but they have the disadvantage of requiring a long length, particularly in its diffuser section. This is because the airstream experiences a drop in pressure below atmosphere as it leaves the turbine blades, and then a positive pressure gradient toward atmosphere as it is discharged from the exit end of the diffuser section. Thus, a continuous increase in pressure exists in the region of the diffuser section. This may cause separation of airflow from the wall of the diffuser, and as a result, a sharp lowering of performance. In order to avoid separation, the diffuser section was made of substantial length so as to have a relatively low total apex angle, in the order of 8.5 degrees.